Preheat your oven to 350°F (175°C) and spray your donut pan with non-stick spray.

In a large mixing bowl, whisk together the pumpkin puree, brown sugar, vegetable oil, and milk until smooth.

In a separate bowl, whisk together the all-purpose flour, baking powder, pumpkin pie spice, cinnamon, nutmeg, and salt.

Gradually add the dry mixture to the wet ingredients, stirring gently until just combined.

Transfer the batter to a piping bag or zip-top bag and fill each cavity of the donut pan about two-thirds full.

Bake for 15-16 minutes, or until a toothpick inserted comes out clean.

Remove the donut pan from the oven and let it cool for about 10 minutes before transferring to a wire rack.

Mix granulated sugar and cinnamon in a shallow dish. Melt butter in a separate bowl.

Brush or dip each warm donut in melted butter and roll in the cinnamon-sugar mixture.